This invention relates to tractors, and more particularly to the combining of a plurality of separable tractor vehicles for operation as a unitary tractor device for powering a common load.
In earthworking projects and other operations of the type in which tractors are employed, there is a continuing demand for increased tractive effort to power larger working implements or to apply more force to existing equipment. Reclamation mining, for example, requires the moving of large volumes of overburden and can be greatly facilitated through the use of large bulldozers and related equipment.
In theory, greater tractive effort can be provided for by scaling up the size of existing tractor designs. In practice, several serious difficulties may be encountered in using this approach to the problem. Very large tractors are extremely expensive to construct and operate, and are therefore limited to certain specialized applications in which high costs can be justified. Further, serious problems arise in connection with transporting a very large tractor from one job site to another.
For these reasons, it is frequently preferable to combine two or more smaller tractors into a unitized assembly for powering a single load. The component tractors of such a unit may be disengaged from each other when necessary for separate use, maintenance, and for shipping purposes.
U.S. Pat. No. 3,661,214 to Peterson et al, assigned to the assignee of this invention, discloses a system wherein multiple tractors are connected by an extensible and retractable cylinder which can be so extended and retracted to vary the relative positions between the tractors to in turn provide for angling of a working implement such as a bulldozer blade, with the maximum angle of the working surface of such blade being approximately 20.degree.. It has been found desirable, to provide high efficiency in earthmoving, to provide that the working surface of the blade is approximately 40.degree. or more from a line transverse of the longitudinal axes of the tractors in the apparatus, i.e. approximately 40.degree. or more from a line perpendicular to the direction of movement of the tractors of the apparatus.
As will be discussed in detail further on, such relatively extreme angling cannot be achieved in the apparatus of U.S. Pat. No. 3,661,214 since the cylinder thereof cannot extend or retract sufficiently to provide such angling, and furthermore, the forward and rearward coupling elements thereof would interfere with the bodies of the tractors, even if the cylinder could achieve such angling.